1. Field of the Invention
This invention relates to active phase shifting circuits and in particular to phase shifters whose shifting characteristics may be accurately controlled.
2. Description of Prior Art
One known type of adjustable phase shifter is described in U.S. Pat. No. 4,087,737. This phase shifter takes the form of an integrator circuit comprising an operational amplifier having a feedback capacitor connected between the amplifier output port and the amplifier inverting input port. A resistor is connected in series between an input terminal and the amplifier inverting input port. Adjustability of the phase shift is achieved by means of a parallel network, connected in shunt with the resistor. The network includes a first capacitor in one branch and a controllable gain amplifier and a second capacitor connected in series in a second branch.
Another phase shifting circuit but of a passive nature involves the use of step attenuators between two hybrids. In such a circuit, a variable loss is employed to generate the applicable phase shift.